1) Field of the Invention
The present invention relates to a fuel supplying apparatus and a fuel injecting apparatus of an internal combustion engine.
2) Description of the Related Art
As methods for supplying a fuel to an internal combustion engine such as a gasoline engine or a diesel engine mounted in a vehicle such as a passenger vehicle or a truck, there are known an inter-cylinder injection method for directly injecting a fuel into cylinders of an internal combustion engine, an inter-intake path injection method for injecting a fuel into an intake path through which an air is supplied to the cylinder of the internal combustion engine, and an inter-cylinder/inter-intake path injection method that is a combination of the two methods, i.e., method for switching over between inter-cylinder injection and inter-intake path injection according to an operating state of the internal combustion engine.
As an internal combustion engine fuel injecting system that performs the inter-cylinder/inter-intake path injection according to the operating state of the internal combustion engine, there is known a system disclosed in, for example, Japanese Patent Application Laid-open Publication No. H7-103048. This internal combustion engine fuel injecting apparatus includes a fuel supplying system, a first fuel injection mechanism including an inter-intake path injector (an injection valve for injecting a fuel into an intake path of internal combustion engine) for the inter-intake path injection, and a second fuel injection mechanism including an inter-cylinder injector (a fuel injection valve for injecting a fuel into cylinders) for the inter-cylinder injection. The fuel supplying apparatus includes a first fuel supply system that pressurizes the fuel in a fuel tank by a low-pressure pump and that supplies the pressurized fuel to the first fuel injection mechanism, and a second fuel supply system that further pressurize the fuel pressurized by the low-pressure pump using the high-pressure pump and that supplies the pressurized fuel to the second fuel injection mechanism. The internal combustion engine fuel injecting apparatus controls injection of the first fuel injection mechanism and that of the second fuel injection mechanism according to a map that is generated based on a fuel supply amount (fuel injection amount), an accelerator opening (accelerator pedal depression amount), and the like. Specifically, ranges on the map is divided into three ranges, namely, an injection range for fuel injection only by the first fuel injection mechanism, an injection range for fuel injection by both the first and the second fuel injection mechanisms, and an injection range for fuel injection only by the second fuel injection mechanism. Based on the map, a control unit controls injection of the first fuel injection mechanism and/or the second fuel injection mechanism according to the operating state of the internal combustion engine.
Meanwhile, a conventional internal combustion engine fuel injecting apparatus includes a high-pressure pump for supplying the high-pressure fuel to the second fuel injection mechanism. This high-pressure pump is constituted so that a cam is driven by rotation of a crankshaft of the internal combustion engine to reciprocate a plunger of the high-pressure pump, and to thereby further pressurize the fuel pressurized by the low-pressure pump. This high-pressure pump continues to be driven by the rotation of the crankshaft of the internal combustion engine even when the control unit controls the inter-cylinder injectors not to inject a fuel, that is, the second fuel injection mechanism is not actuated. Therefore, pulsation occurs when the high-pressure pump absorbs the fuel from the second fuel supply system or returns an excessive fuel to a fuel tank and the like. This pulsation fluctuates a pressure of the fuel in paths of the second fuel supply system and the first fuel supply system, i.e., fluctuates a fuel pressure. This pulsation fluctuates of the fuel pressure is propagated to the first fuel injection mechanism. The control unit controls an injection timing and an injection amount of the fuel injected from the first fuel injection mechanism into an intake path of the internal combustion engine according to the operating state of the internal combustion engine. However, the propagation of the pulsation to the first fuel injection mechanism may possibly make it difficult or impossible to inject the fuel of an injection supply amount determined based on the operating state of the internal combustion engine, from the first fuel injection mechanism. In other words, the fuel in a fuel supply amount by which the fuel is to be supplied to the internal combustion engine may not properly be supplied from the fuel injecting apparatus.